The present invention relates to a method of ensuring against tampering in an electrical system which consists of intercommunicating electrical devices, and also to electrical circuits and systems capable of implementing this method (and thus gaining protection against theft or tampering).
A large number of machines commonly used in daily life contain electrical systems of the above mentioned type which allow correct operation of such apparatuses. Automotive vehicles are one important example.
An electrical system for command and control of electrical devices in an automotive vehicle which has a main central control unit in communication therewith is known from patent application PCT WO 90/10559 for example, which is hereby incorporated by reference. Such electrical devices comprise at least one electrical operation member and an electronic block for command and control.
It is clear that tampering with the electrical system could result in great damage to the equipment and/or its users.
A method for ensuring an integrated circuit against unauthorized use and/or copying is known from U.S. Pat. No. 4,766,516, which is hereby incorporated by reference. In accordance with that document, an integrated circuit designed to provide a particular circuit function has at least one additional circuit element not contributing to performance of these circuit function.
This circuit element assumes the form of a subcircuit for control codes and inhibits operation of the remaining part of the integrated circuit unless it is addressed by means of its control code. The control code subcircuit is at least partially formed of a Focused Ion Beam (FIB) or equivalent rays. Part of the control code subcircuit elements can then be formed with apparent functions which are different from their real functions by using again, for example, a FIB.
This method is thus based on the idea of camouflaging the control code in such a manner that copies, if any, could not be used. The techniques for achieving this can all be applied only during production and in any case before assembly and also require very sophisticated equipment.
The purpose of the present invention is to provide a simple and economical way to implement anti-tampering method for electrical systems.
This purpose is achieved through the anti-tampering method which, through sending and/or reception of identification codes, at least one of the devices in an electrical system is capable of checking whether the system has been tampered with and disables at least its own operation, and preferably the operation of the system.
In terms of the devices employed, the purpose is achieved through the addition to a circuit of a control section which does not contribute to the circuit function, but which is designed to enable and disable operation of the circuit. The control section will have a means of communication which is designed to receive identification codes from at least one external transmitter, a memory to memorize the given identification codes, a comparator designed to compare the codes received with the memorized codes and to emit a result signal corresponding to the result of the comparison, and a selector which enables and disables operation of the circuit depending on the result signal. This circuit and control section may be integrated circuits, but this is not necessary.
An electrical system designed according to this invention is particularly useful in vehicles, where a circuit as described above would automatically check identification codes of the electrical system as soon as the system is switched on.
In an electrical system comprising a plurality of electrical devices, the devices are identified by identification codes memorized in respective control sections and interconnected by means of at least one transmission means. By means of sending and/or reception of the identification codes at least one of the devices is capable of checking whether the system has been tampered with and that at least one said device (preferably all) disables its own operation, the user of the system will be immediately alerted.
By memorizing the identification codes in non-volatile memories programmed only once, customization of the control devices is extremely simple to provide after production of the circuit and executable by means of simple electrical circuits.
Even if the identification code is not camouflaged, the need to replace all the control sections for full operation of the electrical system is in itself a sufficient deterrent against tampering.
Such a method lends itself to use as an anti-theft device, for example for vehicles. Indeed, normally in a vehicle there is a central unit which, after execution of an identification procedure (insertion of the correct key for example), permits starting of the vehicle and checking of the electrical devices connected thereto. The thief is thus forced to disconnect and then replace the central unit with another one. Of course if the electrical devices can be activated only by the central unit associated therewith, e.g. by means of the same identification code, it will be necessary to replace the electrical devices subsequently. This can be considered a good deterrent due to the necessary cost and time.
Thus, in accordance with another aspect, the present invention also relates to an anti-theft method which utilizes the anti-tampering method above to prevent theft of a vehicle. It also relates to a vehicle ensured against theft which has an electrical system capable of implementing such a method.